Correct, tired water pump will effect flow. jobber thermostat will not bypass to heater core properly as I have read and experienced. took a while but I eventually got it all to work together.

 

ok i have the thermo on the left, is that the OEM one, or the bad one?

 

the one on the left is OEM the one on right is aftermarket (stant)

 

ya i messed up, i have the thermo on the right... well ****! do you think thats what my problem is? little heat outta my vents if im moving, barley any defroster and floor heat... and the lower the fan speed the hotter the air i get...

flushed heater core, cleaned squirrel cage. checked blend door.... well watched it complete a cycle(from cold to warm, and the shaft connected to the motor turned no problems)

what else is there for me to do? im pulling my hair out, and brushing popsicles off my A$$... Nickg do you think it could be the thermostat? i just changed it in april, i have the thermo on the right...

 

my problem was the heater core, i changed that, took a day but fixed the problem. i got a cummins thermostat and seems to be warming up better now that its in the negatives now. ill be closing a bit of the blender door next.

 

It is possible it is the heater core, especially if its orginal and the coolant flushes were neglected, but I did have a NEW heater core(I put a 2nd new one in a yr later thinking that it was faulty!) and the Stant thermo and heat was ok around town, but hit the hiway and I'd freaking freeze, I then proped the re-circ door open and that drastically improved heat, but still not perfect, edventually I bought an OEM stat, it cost 125$ locally, and that was from cummins, it cycles more than the stant does, but heat output is amazing compared to the STANT brand, what was happening in my case (theory) OEM style thermo re-directs the coolant through the heater core better, than the stant, so because of poor coolant movement the air passing over the heater core would wick away the heat faster than the coolant was being pushed thru the core.

another possibility for poor heater performance is if your evaporator core is plugged up, this will result in little to no air flow thru the heater core, typically the fan sounds like its spinning fine BUT you have little air flow out any of your vents, if sitting in drv seat you should feel air in your hand all the way back to your face. (place hand in front of vent then move hand backwards)

 

I just re-read this entire post again, there was someone who posted he had a 3rd gen stat, I have seen a 3rd gen stat and can say with certainity while it might fit it will not work, as it is smaller in depth, and does not have a plate on the bottom to re-direct coolant.

 

alright so it looks like im gonna be replacing my thermostat AGAIN.... funny thing is... i replaced it the first time because i wasnt getting enough heat.

i just might drill a hole in my heater box first, and take a look at my evap and heater core. as well as the blend door before i waste money on a new thermo

 

no need to drill a hole, just pull the fan out (3 bolts) and you can look up in there, its a tight fit, but the evap core is visable, hopefully it does not look like mine did, if it does a bottle of electrical contact/brake clean will wash it off, easily, just get a low fume type as it stinks the high heavens

mine looked like this! I had virtually no air flow thru the vents

 

ok i just washed out my heater core and WOW what a world of a difference. i had some guy flush my radatior and heater core back in april, but guess he didnt do a good job! (there goes $100) but find out what direction the water flows (hose coming from engine block is supply, and the other hose is the return). undo both hoses, hook your garden hose up to the return, and just let the water flow... i would turn it on, then stop. then turn it on again, did this several times. do that to both sides, if your still having problems with it you can add some chemicals and let em sit, but mine wasnt that bad!

 

I believe I got this problem this year after changing the radiator and water pump this summer as I know I had no heating problems last winter. OK, I read through all 4 pages of this thread and here's what I have checked. Today our outside air was about -8 deg C (18 F), with maximum heat on, fan at high speed, my temperature at the driver side vent was 25 C (77 F) with engine fully warmed up and showing about 80 C (176 F) on the dash gauge. Shooting the heater hoses at the firewall (engine side) with my infrared temp gun, the inlet hose to the heater recorded about 80 C, the outlet hose 77 C. This tells me (I think) that I have decent flow through the heater core (with heater fan on high at the time). Then I switched over to Max AC leaving the heat and fan speed setting at maximum and after a few minutes the temperature at the driver side vent was recorded at 45 C (113 F). I realise that some recirculation takes place at Max AC, but it also tells me (I think) that there is no problem with the heater core, because if there was, there should have not been such a change in temperature at the vent. I know there are smarter guys out there than me, hopefully someone can steer me in the right direction for actions I should take to correct this problem.

 

My heater core is bypassed. I'll have to pressure check the core to find out if it leaks or if it was disconnected to get colder air.

 

I installed a heater core flush tap on the heater return line. I found my heater core was hard to remove the air . I found I had to open the flush tap with the front of the truck up hill some.I did get more heat after removing the air trapped in the core. I could hear it move when I started the engine.